WEDNESDAY, June 18, 2014 (HealthDay News) -- Some U.S. jurisdictions are now requiring a doctor's OK for people to carry a concealed gun, but a new survey suggests many doctors aren't comfortable with that role.

The survey, of 222 North Carolina doctors, found that 21 percent had been asked in the past year to sign "competency permits" for patients to carry a concealed weapon. By signing, the doctor attests to the patient's mental and physical ability to safely carry a firearm.

The problem, experts say, is that there are no standard definitions of physical or mental "competence," and doctors have been left to make those calls on their own.

"There are no guidelines on this," said Dr. Adam Goldstein, the senior researcher on the study and a professor of family medicine at the University of North Carolina at Chapel Hill.

Laws vary, but in many U.S. states people who apply for a permit to carry a concealed weapon have to be deemed physically and mentally competent. In some jurisdictions, the sheriff's office contacts the applicant's primary care doctor.

Goldstein said he got his first such request soon after the December 2012 massacre at Sandy Hook Elementary School in Newtown, Conn., when 20-year-old Adam Lanza shot and killed 20 children and six adults.

That tragedy renewed attention on the issue of gun control, but Goldstein said he wasn't expecting to be involved in judging people's competency to carry firearms. Nor were his colleagues who also started receiving requests from the county sheriff.

"It actually surprised us," Goldstein said. Unsure how to handle the requests, the doctors looked for some guidance in the medical literature, and found none.

That eventually led to the new survey, reported in the June 19 issue of the New England Journal of Medicine.

"We wanted to see what our colleagues around North Carolina are thinking about this," Goldstein said.

His team sent surveys to 600 primary care doctors and psychiatrists in the state, and got responses from 222. Overall, 59 percent said they doubted their ability to judge whether a patient was physically "fit" to carry a gun safely, and 47 percent doubted they could judge a patient's mental fitness.

A full 84 percent said those judgment calls should be made by professionals specifically trained to do so.

Yet, of the doctors who'd gotten requests to do competency evaluations, 79 percent had signed off on them, the study found.

"We were a little surprised by that, and a little worried," Goldstein said.

He stressed that patients given the approval may well have been competent. But the concern is, doctors have no standards to go by.

"This connects to a broader issue: What is the clinician's role in people's Second Amendment rights?" said Jeffrey Swanson, a professor of psychiatry and behavioral sciences at Duke University in Durham, N.C.

Swanson, who studies firearm laws and violence prevention, said a doctor can judge whether a patient has any physical health conditions.

"But how do they judge whether a physical infirmity prevents the safe handling of a gun?" Swanson said.

And judging mental competency, he added, gets even trickier. It's notoriously difficult for even trained psychiatrists to predict whether an individual with mental health problems poses a danger to others, Swanson noted.

A primary care doctor, he said, "shouldn't be asked to opine on who's going to become violent."

Both Swanson and Goldstein said guidelines -- including standard definitions of mental and physical competence -- are needed.

But just who would formulate those guidelines is unclear. The American Medical Association and American College of Physicians -- two national groups representing doctors -- declined to comment on the survey.

There are also issues beyond technical definitions of competency. In the survey, 59 percent of doctors worried that refusing to sign off on a request would "cause problems in the doctor-patient relationship."

Some doctors may worry about legal problems, too, Swanson noted. If, for example, someone deemed competent kills or injures another person, could the doctor be held liable?

"If over 20 percent of the doctors in this survey have been asked to sign competency permits, then it's a big issue," Goldstein said. "But it's an issue that most people are probably unaware of. We hope this study can inform a conversation."

SOURCES: Adam Goldstein, M.D., MPH, professor, family medicine, University of North Carolina School of Medicine, Chapel Hill; Jeffrey Swanson, Ph.D., professor, psychiatry and behavioral sciences, Duke University School of Medicine, Durham, N.C.; June 19, 2014, New England Journal of Medicine